Blogroll

Tuesday, 17 June 2014

An open collector or open drain output is an output from a transistor with no connection on collector as shown in the following image.

This circuit will work. only if an external pull up resistor is added. One end of the resistor is connected to the collector and the other end is connected to the positive voltage.

When the transistor is on( Control Signal is HIGH ), it puts ground on the output (Vout = 0 ). When the transistor is off ( Control Signal is LOW ), since one end of pull up resistor is connected to the positive voltage, output will be 1 ( Vout = 1 ). Main advantage of the open collector circuit is, by varying the value of resistance, we can change the output current. Also it is compatible with I2C communication protocol. Usually the pull up resistance will be 10K, if it is used for General Purpose Input/Output (GPIO) and the pull up resistance will be 2K, if it is used for Inter-Integrated Circuit (I2C).

IMPORTANT NOTICE

All the circuits, published in this blog is only after testing and getting proper results in my private lab. When you try these circuits, you should check the supply voltage, polarity of components, presence of childrens nearby and shorts in the circuits. This website will not be responsible for any harm happened to you or your components caused by your carelessness.